1. Field of the Invention
The present invention relates to a sensor control device and a sensor control system that measures, for example, the concentration of a specific component in an object measurement gas such as an intake charge mixture of an internal combustion engine and that is suitable for use in compensating an output signal of an oxygen sensor.
2. Description of the Related Art
In an internal combustion engine in recent years, the control of an air-fuel ratio that is a ratio of fuel to intake air, and more specifically, the control of a ratio of fuel to oxygen included in the intake air is generally performed for the purpose of improving fuel economy and reducing harmful substances included in exhaust gas. When performing this control, it is necessary to measure the volume of the intake air. For example, a method is known using an air mass flow sensor for measuring the volume of the intake air. The air mass flow sensor is used in an internal combustion engine equipped with an intake throttle valve and may be used to measure the cylinder air intake volume, which changes according to an operation state.
On the other hand, an intake throttle valve is not provided in a diesel engine, a direct-injection gasoline engine, and the like, and the volume of cylinder air intake volume is basically constant. Moreover, in a diesel engine having an exhaust gas recirculation device (hereinafter referred to as an “EGR device”) for recirculating a part of the post-combustion exhaust gas into the intake air, the ratio of oxygen included in the intake air changes due to an amount of recirculating exhaust gas (hereinafter referred to as “EGR amount”). In other words, the amount of cylinder oxygen intake changes.
In this case, the air-fuel ratio is difficult to precisely control using only the air mass flow sensor described above. That is, in control of air-fuel ratio using only an air mass flow sensor, the amount of cylinder oxygen intake is calculated assuming that the ratio of oxygen included in the intake air, for example, is the same as the ratio of oxygen included in the atmosphere. The amount of cylinder oxygen intake may not be accurately calculated because the ratio of oxygen included in the intake air changes in an internal combustion engine equipped with an EGR device.
To solve the above described problems, an oxygen sensor that measures oxygen concentration included in the intake air is used, and a technique that calculates an amount of cylinder oxygen intake has been proposed (see, for example, JP-A-H02-221647). In this technique, an amount of cylinder oxygen intake is calculated by measuring the volume of cylinder air intake with the air mass flow sensor and further measuring the oxygen concentration of the intake air with the oxygen sensor. For control of the air-fuel ratio, a feed-forward control is considered to provide good results in which an amount of fuel injected into the cylinder or an intake port is controlled according to the amount of oxygen that is calculated as described above.
[Patent Document 1] JP-A-H02-221647
3. Problems to be Solved by the Invention
It is known that it is necessary to compensate for a change in an output value resulting from, for example, deterioration in the oxygen sensor in a case where the oxygen sensor is used as described above. Especially, in a case where the oxygen sensor is arranged only in an intake system, high oxygen sensor accuracy is required. Further, the necessity for compensation is increased, as compared to the case where oxygen sensors are arranged in the intake system and a non-intake system. For this reason, the technique, disclosed in JP-A-H02-221647 also compensates an output value of the oxygen sensor after the internal combustion engine stops.
However, electric power is always consumed when compensating the output value of the oxygen sensor, and in a case of a vehicle, the electric power is supplied from a mounted battery. When the electric power of the battery is not sufficient in the case where the compensation is performed after the internal combustion engine stops, as disclosed in JP-A-H02-221647, there is a concern that the compensation may not be performed in an accurate state. More particularly, this might be the case where a heater of the oxygen sensor may not be sufficiently driven, or the case where a temperature of the sensing element may not be precisely controlled. Furthermore, even in a case where the compensation is performed, there is a concern that the battery is easily drained because the electric power of the battery is consumed.